The long-term objective of this project is to understand how morphogen gradients pattern the cerebral cortex and other tissues during development. Morphogen gradients are fundamental to animal development, and morphogen defects are primary causes of human birth defects and malformations of the cortex. Nonetheless, tremendous controversy remains about the mechanisms by which morphogen gradients act, which limits our understanding of these human disorders. For the most part, this controversy revolves around a single issue - the inability to distinguish morphogen activities that do not depend on cell-cell communication (the "classical" model) from those that do. To date, insight into this issue has relied on heroic studies using traditional dissociated cell cultures, which are limited both in terms of experimental efficiency and as models of natural morphogen gradients. However, a microfluidic culture device has the potential to address these limitations. This microscale device generates precise and continuous biomolecular gradients with different profiles onto cells, and is designed for time-lapse microscopy. These features should provide several biological and practical advantages over traditional cultures for modeling and studying morphogen gradients. Preliminary studies with cortical precursor cells (CPCs) confirm the promise of this system, but have also identified device design features that need to be optimized in order to answer the basic question driving this proposal - which CPC responses in the normal cortex are determined solely by extracellular morphogen concentration, and which are not? The goals of this R21 proposal are to fabricate optimized microfluidic devices for culturing CPCs (Aim 1) and to develop real time assays with single cell resolution in order to efficiently study CPC responses as functions of morphogen concentration, gradient profile, cell density, and time (Aim 2). To achieve these goals, a multidisciplinary team with primary expertise in bioengineering (Noo Li Jeon, the developer of the original gradient-generating device), morphogen gradients (Arthur Lander) and cortical development (Edwin Monuki) has been assembled. If successful, this proposal should not only advance our understanding of cortical development and malformations, and of morphogen gradients in general, but should also provide a versatile microfluidic tool with a wide range of basic and clinical applications.